Electrochemical Deposition,Structures And Properties Of The Two-dimensional D-A Type Conjugated Polymer Organic Semiconductor Films

The?-electrons in the conjugated polymers can flow along the conjugated system.However,it is difficult for the?-electrons to transport between intra-macromolecules,and the delocalizing range of?-electrons over the inter-macromolecule is still relatively limited because of the long-distance-disorder,partial crystallization,and the imperfect crystal in the conjugated macromolecular condensed structure as well.For those D-A(Donor-Acceptor)type conjugated polymers,which have both electron-rich donor units and electron-deficient acceptor units in their molecular chain structures,the D-A structure of the conjugated polymer is not only contribute to delocalization of the conjugated?-electrons extent to a far distance along the polymer conjugated system but also advantage to their transport among adjacent molecular chains.The effectively control and adjustment of the electron energy level structure were capable of achieving for those D-A type conjugated polymers by theoretical calculations and molecular design methods using different types of D-A units,and some novel organic semiconductor materials with different energy band gaps and conductivity were also made.Therefor,these researches on their preparation technology,structure and photoelectrochemical properties of the semiconductor polymeric materials with different D-A unites take a great role for understanding the charge transport mechanism in D-A type polymers and developing novel organic semiconductor materials and devices in academy and application.In this paper,4,5-diamino-orthodicyanide benzene and diphenylamine-4-sulfonate acid sodium were used as monomer materials,and the effect of process parameters on properties of the polymer films deposited was researched by Cyclic Voltammetry(CV)and potentiostatic techniques.Two organic semiconductor polymers with different D-A structures,which one is insoluble and another is soluble,were successfully prepared.Their crystal structure was characterized by X-ray diffraction(XRD);The texture and crystal geometric morphology of these polymer films were observed by metallographic microscope and SEM,respectively;Their chemical composition and optical properties were investigated by UV-visible spectroscopy and Raman spectrum,respectively,and the optical band gap were obtained by Tauc plot calculation based on their optic absorption properties;their electrochemical properties of the polymers deposited were studied using the CV and EIS techniques,the thermal properties were investigated by DSC and TGA,respectively.The main conclusion are concluded as follows:(1)Solvent composition in electrolyte solution and CV scanning rate have a significant effect on its electrochemical polymerization and the polymer films'properties and structures during the electrochemical deposition of water-insoluble monomer 4,5-diamino-orthodicyanide benzene.The insoluble monomer has the highest reaction activity when the volume ratio of acetonitrile/water solvent is 2:1 in the electrolyte solution.With the increase of the CV scanning rate,the current and potential of oxidation peak increase slightly during the electrochemical oxidation polymerization of the monomer.The E_g~electrochemlectrochem and E_g~opp have the smallest value for the polymer film deposited using the solvent of acetonitrile/water volume ratio 2:1and the CV scanning rate 30 mV/s.(2)Solvent polarity in electrolyte solution and CV scanning rate have a grate effect on its electrochemical polymerization and the polymer films'structure and the properties during soluble monomer diphenylamine-4-sulfonate acid sodium electrochemical reaction,and in pure acetonitrile electrolyte solution a green polymer film sample can be obtained on the surface of the ITO working electrode by CV;however,the polymer film fail to be deposited on ITO surface when acetonitrile-water,N-N dimethylformamide,tetrahydrofuran were used respectively as the solvent of the electrolyte during electrochemical polymerization of diphenylamine-4-sulfonate acid sodium monomer.In the same time,with the increase of the CV scanning rate,the current and potential of the oxidation peak increase slightly.The E_g~electrochemlectrochem and E_g~optpt values of the polymer film were the smallest electrochemical deposited at 50 mV/s CV scanning rate.(3)The water-insoluble conjugated polymer with a two-dimensional D-A structure,poly(4,5-diamino-orthodicyanide benzene)exhibits the conductive characteristic of N-type semiconductor materials,while the water-soluble poly(diphenylamine-4-sulfonate acid sodium)conductive polymer shows the conductive characteristic of P-type semiconductor materials.(4)The poly(4,5-diamino-orthodicyanide benzene)film prepared by electro-chemical deposition has a low energy band gap,and the minimum values of E_g~electrochemlectrochem and E_g~optpt are 0.84eV and 1.03eV,respectively;for water-soluble poly(diphenylamine-4-sulfonate acid sodium)films prepared in non-aqueous systems the minimum values of E_g~electrochemlectrochem and E_g~optpt are 1.51eV and 1.74eV,respectively.(5)In the electrolyte solution,the polymer film of 4,5-diamino-orthodicyanide benzene has a needle-like geometric crystalline junction morphology with complete crystal structure and homogeneous polycrystalline features,while the crystal shows the scaly geometric characteristics for the polymer film from diphenylamine-4-sulfonate acid sodium electrochemical deposition.(6)The two conjugated conductive polymers both poly(4,5-diamino-orthodicyanide benzene)and poly(diphenylamine-4-sulfonate acid sodium)from electrochemical deposition have good redox reversibility,good thermal stability,and their thermal decomposition temperatures are 400?and 325?,respectively.